Acid copper plating bath



United States Patent 3,101,305 ACID COPPER PLATING BATH Emil Roth andGregor Michael, Bielefeld, Germany,

assignors to Riedel & Co., Bielefeld, Germany, a German firm No Drawing.Filed Mar. 12, 1958, Ser. No. 720,824 Claims priority, applicationGermany Mar. 16, 1957 6 Claims. (Cl. 204-52) This invention relates toacid baths for producing brilliant copper levelling coatings.

The state of the art of acid bath copper plating is fhar-acterized bythe use of two diiferen-t forms of electroyte:

(1) An electrolyte giving a high and uniform polish but withoutappreciable levelling or smoothing effect.

(2) An electrolyte with good levelling or smoothing properties, but notgiving a brilliant or mirror finish or lacking a uniform brillianteiiect over a wide range of current densities.

Neither of these types of bath, however, satisfies th technicalrequirements with regard to economizing in grinding and polishing costs.

The present invention relates to a class of substances which produce inacid copper-plating baths capable of imparting to articles treatedtherein a brilliant finish but no levelling or smoothing effect, asurprising smoothing or levelling action Without affecting theoriginally obtained, uniform brilliant finish and without unfavorablyinfluencing penetration in depth of the bath. The smoothing effect is sopronounced that grinding marks com pletely disappear after deposition ofa copper coating of a thicknses of 26 1. only. Such an effect is notattained in any of the known sulfuric acid bright copper-plating baths.They require a thickness of the copper coating of at least 42a in orderto completely cover and eliminate, i.e. to level the microscopic cracksobtained on grinding the surface to be copper plated.

According to the present invention an acid bath for the preparation ofhighly brilliant, smoothing or levelling copper coatings is providedwhich bath is characterized by the feature that it combines the use ofbasic brightening agents having in their molecule at least one group ofthe formula wherein X represents a member selected .firom the groupconsisting of the hydroxyl group, the carboxyl group, the sulfonic acidgroup, and a canboxylic acid ester group, While 11 is an integer between1 and 10,

and wherein such groups predominate, with the addition of specificthiourea derivatives as smoothing or levelling agents.

It has been observed that thiourea and certain derivatives of thioureain acid, bright copper-plating baths, produce a moderate, levelling orsmoothing elfect.

The present invention consists in using primary condensation products ofthiourea with aliphatic aldehydes, tor instance, with formaldehyde. Suchderivatives of thiourea have a considerably greater smo oth-ing orlevelling effect than the known thiourea compound heretofore used forthis purpose.

in the preparation of such primary thiourea condensation products, thetemperature at which they are prepared, should not be too high sincethere is otherwise the danger that insoluble resins will be produced.The optimum temperature conditions for the preparation of the thioureacondensation products are between about C. and about C. Depending on theexact temperainure, reaction time, and catalysts employed, the followingaddition pnoducts can be obtained:

wherein m indicates an integral number.

However, the excellent levelling or smoothing properties of thesethiourea derivatives are utilized only when employing said compounds incombination with particular, primary brightening agents which alone,i.e. by themselves, pnoduce no levelling or smoothing efiect.

Such primary brighteners may be any of the above mentioned compoundscontaining one or more groups of the formula NS-(CH2)DX 1 'wherein Xindicates a member selected from the group consisting of the hydroxylgroup, the carboxyl group, the sulfonic acid group, and :a carboxylicacid ester group, while n is an integer from 1 to 10.

Preferred brightening agents of this type are dithiocarbarnic acidderivatives of the formula R and R indicate hydrogen, aliphatic, oraromatic residues,

n indicates an integer from 1 to 10, and

X indicates a member selected from the group consisting of the hydroxylgroup, the carboxyl group, the sulionic acid group, and a carboxylicacid ester group.

Especially suitable brighteners of this type are, furthermore,heterocyclic nitrogen compounds such as compounds of the pyridine,pyrimidine, triazine, tetrazine, pyrazole, imidazole, triazole,pyIr-o-le, quinoline, cinnoline (5,6- benzopyridazine) series and thelike in which one or more hydrogen atoms linked to carbon atoms aresubstituted by the radical wherein X represents the hydroxyl group, thecarboxyl group, or another water soluble group of a different anioniccharacter. Such a group S-(CH ),,X need not necessarily occupy an endposition in an aliphatic side chain. Compounds of the following formulasare especially suitable examples of this group of primary brighteners:

Pyrazine-3,'6-dithioglycolic acid no o-s-orn-on-pna on3-on on2 so' on onI on N 3,6-dimercaptoB-hydroxy propyl pyrazine The following comparativeexamples serve to illustrate the present invent-ion and the effectsachieved thereby without, however, being limited thereto.

Example 1 (a) A sheet of iron or steel is ground to a zero polish and isthen copper plated in a bath of the following oompos-ition (in g. perliter):

210 g. of copper sulfiate CuSO .5H O,

60 g. of concentrated sulfuric acid,

5 g. of an alkyl polyglycol known to the art as wetting agent,

0.3 g. of ethyl dithiocarbamoyl propionic acid ester, and

0.15 g. of hydrochloric acid,

at 4 amp/sq. dm. and 20 C. for 30 minutes. The resulting copper platedsurface of the sheet is bright. The grinding marks, however, have notbeen eliminated.

(b) The plating is repeated under the same conditions with the abovementioned bath solution to which, however, 0.02 g. of the acid-solublethiourea-formaldehyde condensation product are added. A copper depositof about 26 4 thickness and a high bri-lliancy is obtained. The grindingmarks are almost completely level-led.

Example 2 (a) A brass sheet previously polished on :a. zero numbergrinding wheel is treated at 4 amp/sq. dm. and at 20 C. for 30 minutesin a bath containing per liter:

210 g. of copper sulfate 011304511 0,

60 g. of concentrated sulfuric acid,

5 g. of an alkyl polyglycol known to the art as wetting agent, and

0.4 g. of pyrazine-3, 6-dithioglycolic acid.

The resulting coating is :bright, but no level-ling or smoothing eifectis observed.

(12) Addition of 0.02 g. of the acid-soluble thioureaformaldehydecondensation product to the above mentioned copper plating solution andexposing the polished brass sheet to said solution under the samereaction conditions produces a copper coating not only of the samebrilli-ancy as produced with the hath given under (a) but also aperfectly smooth and levelled coating so that the grinding marks from azero number wheel are no longer visible although the thickness of thedeposited copper coating is only 26p.

The smoothing and levelling eifects achieved by suchthiourea-formaldehyde condensation products are considerably improved byreplacing said condensation products by products obtained bysimultaneous condensation of thiourea, formaldehyde, and polyaminocompounds containing at least two amino groups.

Such condensation products are characterized by containing not onlythiourea moieties bridged by methylene moieties but also diaminemoieties bridged by methylene moieties. Thereby, chain structures or twoto three dimensionally cross-linked structures are obtained. Thesimplest condensation products of this type correspond approximately tothe following formula C Hzwherein To prepare these condensationproducts, the required amounts of thiourea, polyamine, and formaldehydeare condensed at a temperature of about 110-130" C. The molar ratio beteen the thiourea and the compound containing at least two amino groups,for instance, melamine, has an optimum value of 1:1, but other ratiosmay be employed, for instance, a ratio of 1:2. The aggressive action ofthe thiourea by such a cocondensation with a polyamine is considerablymitigated and its inhibitory effect is favorably adjusted for thepurpose in view.

Instead of melamine, other substances containing at least two aminogroups can be used as reaction component in such co-condensationreaction, such as diamino azobenzene, diamino diphenylamine, diaminodiphenylurea, diamino stilbene, urea, o dianisidine, o-toluidine,phenylene diamines, 2,4'-diamino diphenyl, parafuchsin, congo red,benzidine, guanidine, benzidine-2,2'-disulfonic acid, diarnino stilbenedisulfonic acid, 1,5-diamin0 naphthalene-3,7-disulfonic acid,naphthalene diamines, homologues and derivatives thereof, and the likepolyarnino compounds.

In co -condensation products, for instance, in the thiourea formaldehydenaphthalene diamine condensation products, the activity of the thioureacomponent is considerably reduced by the presence of less active groups.In addition, partial substitution of thiourea moieties by naphthalenediamine moieties produces condensation products of larger molecularsize, which are particularly suitable for producing a uniform smoothingand/ or levelling effect even at elevated temperatures.

The known fact that copper is inhibited with difiiculty,

especially at elevated temperature, can readily be compensated for byadding to the copper plating bath larger inhibitor molecules of aspecific degree of condensation, while preserving its activecharacteritsics due to the presence of N( JS-- I groups. Copper bathscomposed in this manner furnish, even at 3540 C., brilliant, excellentlylevelling copper coatings, while identical baths on a basis ofthioureaformaldehyde condensation products alone operate only attemperatures of 25 C. and lower.

The following examples serve to illustrate the use ofthiourea-formaldehyde-polyamine condensation products as smoothing andlevelling agents according to the present invention without, however,limiting the same thereto.

Example 3 A bath of the following composition in g. per liter is usedfor copper plating:

Copper plating is effected with a current density of 1-6 amp/sq. dm. at15-35 C. Bright copper coatings of a thickness of 26 of sufiicientbrilliancy and good levelling properties are obtained wherein the marksof a No. 0 grinding wheel are completely eliminated.

Example 4 A copperplating bath of the following composition in g. perliter is used:

200 g. of copper sulfate CuSO .5H O, g. of concentrated sulfuric acid, 8g. of an alkyl polyglycol known to the art as wetting agent, 0.4 g. ofpyrazine-3,6-dithioglycolic acid, and

s 0.04 g. of an acid-soluble thiourea-formaldehyde-diamino diphenylaminecondensation product.

Copper plating is efiected at current densities between 1-6 amp/sq. dm.and at a temperature range between C. and 40 C. Brilliant, effectivelylevelling copper coatings are obtained thereby.

When replacing in the above mentioned bath thethiourea-formaldehyde-diamino dipheny-lamine condensation product by0.02-0.04 g. of an acid-soluble thioureaformaldehyde condensationproduct, the same brilliancy and leveling effect are obtained. However,the temperature must be kept at C. or, preferably, lower when operatingat a current density range between 2.5 amp./ sq. dm. and 6.0 amp./ sq.dm. At higher temperatures, such as between 25 C. and 40 C. the coppercoatings are dull and no smoothing effect is observed.

It is understood that other brightening agents than those used in thepreceding examples may be employed provided they contain the groupN(:3S-(CHr) n-X mentioned hereinabove. For instance, other esters ofdithiocarbamoyl alkyl carboxylic acids than the ethyl dithiocarbamoylpropionic acid, such as propyl, butyl, and other alkyl, aryl, or aralkyldithiocarbamoyl propionic acid esters, or ethyl dithiocarbamoyl acetic,butyric, valeric, capric and the like acids and their esters providedthese compounds are soluble in the copper plating bath.

Other heterocyclic compounds with nitrogen as hetero atom in theirnucleus than pyrazine-3,6-dithi oglycolic acid,3,6-dirnercapto-fi-hydroxy propyl pyrazine may also be used asbrightening agents. 7

Such brightening agents are known to the art and their use in copperplating processes are known to the art.

The thiourea-formaldehyde condensation products used in Examples 1 and 2as well as the thiourea-formaldehydepolyamine condensation products usedin examples 3 and 4 may be replaced by other condensation productswherein other aldehydes are employed than formaldehyde. The conditionsof preparation of such condensation products must be such that theproducts are sufficiently soluble in the copper plating bath.

As stated hereinabove, addition of thiourea-aldehyde condensationproducts or thiourea-aldehyde-polyamine condensation products to copperplating baths has a number of advantages and more particularly permitsto produce perfectly smooth and levelled copper surfaces in a thicknessof about 26a only. In addition thereto it was found that polishing ofthe precipitated thin copper coating is not required. As a resultthereof it is possible to continuously subject suitable sheet materialand the like articles to copper plating according to the presentinvention and immediately thereafter to nickel plate such copper platedsheets and the like articles without any intermediate treatment.

Furthermore, the copper plating baths according to the present inventionpermit operation with a current density of 6 -amp./ sq. dm. or even morewhile heretofore current densities of 4 amp./ sq. dm. usually could notbe exceeded.

The amounts of the thiourea-aldehyde condensation products or ofthiourea-aldehyde-polyamine condensation products to be added to thecopper plating bath may, of course, vary depending upon the compositionof the bath and the composition of the smoothing and levelingagent.Amounts between about 0.001 g./l. and about 0.5 g./ l. have provedsatisfactory. The preferred amounts are between about 0.01 g./l. andabout 0.04 g./l.

The brightening agents, i.e. the dith-i'ocarbamic acid compounds andsimilar heterocyclic compounds are added as is known, in amounts betweenabout 0.01 g./l. and about 0.5 g./l. although they are not "limited tosuch amounts.

Of course, in place of alkyl polyglycols used as wetting agents, theremay be employed other wetting agents compatible with the copperpl-atingbath. Especially suitable are wetting agents based on ethylene oxide,i.e. polyglycol compounds and the like. Sulfonated wetting agents haveproved of advantage due to their increased solubility in water. Ingeneral, non-ionogenic wetting agents, such as wetting agents with etherbridge bonds have proved to be useful additives.

Of course, many other changes and variations in the composition of thecopper plating bath, in the brightening agents employed, in thethiourea-aldehyde condensation products and thethiourea-aldehyde-polyamine condensation products used as smoothing andlevelling agents according to the present invention, theelectroprecipitation conditions, such as current density, temperature,and duration, and the like may be made by those skilled in the ant inaccordance with the principles set forth herein and in the claimsannexed hereto.

We claim:

1'. An acid copper plating bath for producing smooth and levelled coppercoatings of high brilliancy, said bath containing, as brightening agent,a basic brightening agent selected from the group consisting ofdithiocarbamic acid compounds of the formula wherein R and R are membersselected from the group consist ing of hydrogen, aliphatic, and aromaticresidues,

X is a member selected from the group consisting of the hydroxyl group,the carboxyl group, the sulfonic acid group, and the carboxylic acidester group, and

n is an integer between 1 and 10,

and heterocyclic nitrogen-containing compounds, at least one of thecarbon-linked hydrogen atoms of said heterocyclic compounds beingsubstituted by the group, X and n in said group representing the samemembers and numbers as indicated above, and between about 0.001 g./l.and about 0.5 g./l. of a levelling agent consisting of an acid-solublecondensation product of thiourea, an aliphatic aldehyde componentconsisting of formaldehyde, and a compound having at least two aminogroups in its molecule.

2. An acid copper plating bath for producing smooth and levelled coppercoatings of high brilliancy, said bath containing per liter about 2-10g. of copper sulfate CuSO .5H O,

about 60 g. of concentrated sulfuric acid,

about 5 g. of an alkyl polyglycol as wetting agent,

about 0.4 g. of pyrazine-B,6-dithioglycolic acid as brightening agent,and

about 0.02 g of an acid-soluble thiourea-formaldehyde condensationproduct as smoothing and levelling agent.

3. An acid copper plating bath for producing smooth and levelled coppercoatings of high brilliancy, said bath containing per liter about 210 g.of copper sulfate CuSO .5H O,

about 60 g. of concentrated sulfuric acid,

about 5 g. of an alkyl polyglycol as Wetting agent,

about 0.3 g. of ethyl dithio'carbamoyl propionic acid as brighteningagent,

about 0.15 g. of hydrochloric acid, and

about 0.02 g. of an acid-soluble thiourea-formaldehyde condensationproduct as smoothing and levelling agent.

4. An acid copper plating bath for producing smooth and levelled coppercoatings of high brilliancy, said bath containing per liter 5. An acidcopper plating bath for producing smooth and levelled copper coatings ofhigh brilliancy, said bath containing per liter about 200 g. pf coppersulfate CuSO .5H O,

about 90 g. of concentrated sulfuric acid,

about 8 g. of an alkyl polyglycol as wetting agent,

about 0.4 g. of pyrazine-3,6-dithioglycolic acid as brightening agent,and

about 0.04 g. of an acid-soluble thiourea-formaldehydediaminodiphenylamine condensation product as smoothing and levelling agent.

8 6. An acid copper plating bath for producing smooth and levelledcopper coatings. of high brilliancy, said bath containing, asbrightening agent, a basic brightening agent having at least one groupof the formula in its molecule, X in said group indicating a memberselected from the group consisting of the hydroxyl group, the carboxylgroup, and a Water soluble group of different anionic character, and 12indicating a whole number between 1 and 10, and "between about 0.001g./l. and about 0.5 g./l. of a levelling agent consisting of anacidsoluble condensation product of thiourea and an aliphatic aldehydecomponent consisting of formaldehyde.

References Cited in the file of this patent UNITED STATES PATENTS2,828,252 Fischer Mar. 25, 1958 FOREIGN PATENTS 762,257 Great BritainNov. 28, 1956 Germany Sept. 3, 1953

1. AN ACID COPPER PLATING BATH FOR PRODUCING SMOOTH AND LEVELLED COPPERCOATINGS OF HIGH BRILLIANCY, SAID BATH CONTAINING, AS BRIGHTENING AGENT,A BASIC BRIGHTENING AGENT SELECTED FROM THE GROUP CONSISTING OFDITHIOCARBAMIC ACID COMPOUNDS OF THE FORMULA